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Highlights • Backpressure adjustable gas turbine combined-cycle is proposed. • Off-design characteristics with different operation strategies are analysed. • Load range with strategy keeping turbine inlet temperature constant is expanded. • Part-load efficiency is improved with a maximum increase of 0.52–1.76%. Abstract Nowadays, power demand and supply of the power grid fluctuate constantly for the increasing proportion of the renewable energy. Improving the operation performance of the gas turbine combined cycle (GTCC) power plant at part-load conditions is becoming a very critical problem. An innovative combined cycle solution, called backpressure adjustable gas turbine combined cycle (BAGTCC) with corresponding operation strategies, is proposed in this paper to improve off-design performance by adjusting turbine backpressure. The off-design calculation models of the combined cycle are built and their reliability is verified. The feasibility of this scheme is analyzed with the Mach number of the gas flow in turbine. Then, the part-load operation characteristics of the topping cycle, bottoming cycle and combined cycle of the GTCC and BAGTCC, operating with two different operation strategies respectively, are analyzed and compared. The simulation results show that, the proposed BAGTCC can broaden the load range, where turbine inlet temperature (TIT) maintains its design value, from 100–82.4% to 100–63.7%. The combined cycle efficiency has been improved significantly in that load range, up by 0–0.52 and 0–1.76 percentage points over the two conventional operation strategies respectively. Furthermore, this solution has the ability to adjust the power distribution of topping and bottoming cycle, which means that the heat-to-electric ratio can be adjusted when the bottoming cycle is involved in heating. The energy saving potential of BAGTCC can be increased by broadening the compressor flow adjustment range. In conclusion, backpressure regulating is an efficient method to improve the part-load efficiency of the GTCC. [ABSTRACT FROM AUTHOR]

To undertake peak shaving tasks, gas turbine combined cycle (GTCC) units often deviate from the design operating point. In order to improve the off-design performance of GTCCs, a dual-recuperated gas turbine combined cycle (DRGTCC) system based on partial recuperation and compressor inlet air heating is proposed in this paper. The operating characteristics of the novel system using the proposed operation strategy are investigated, and the effects of pressure drop in recuperators and ambient temperature on system performance are discussed. The results indicate that, compared with the GTCC system, the DRGTCC system has higher turbine inlet temperature (TIT) and turbine expansion ratio at the same power output, and the performance has been improved especially at lower power outputs. When the inlet temperature of the compressor is increased from 0 °C to 45 °C, the air mass flowrate can be regulated between 46.0% and 100% of the design value. The combined cycle efficiency of the DRGTCC system is improved by 2.55 percentage points at 45.5% design combined cycle load. Moreover, the sensitivity analysis shows that the system performance decreases with the increase of the pressure drop in recuperators, and the ambient temperature affects the load regulation range and efficiency. • A dual-recuperated gas turbine combined cycle system is proposed. • The bottoming cycle can actively participate in load regulation. • Part-load characteristic prediction model considering the new operation strategy is designed. • Strategy combined multiple regulation methods achieves better part-load performance. • Sensitivity analyses of pressure drop and ambient temperature are carried out. [ABSTRACT FROM AUTHOR]

• A SOFC-IGT integrated distributed cogeneration system with zero CO 2 emission is proposed. • The operating parameters are optimized using multi-objective genetic algorithm. • The heat exchanger network synthesis is conducted. • The heat exchangers in the specific designs are designed and optimized. • The performances of the designs are verified and compared for specific application scenarios. Solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system is an efficient and potential method for distributed energy supply. The system layout, component operating parameters, system-level heat integration, component selection and design, etc., determine the system performance. To further improve the performance and achieve zero CO 2 emissions, a ambient-pressure solid oxide fuel cell-inverted gas turbine (SOFC-IGT) hybrid system with CO 2 capture using oxy-fuel combustor was proposed. With the aid of partial-load component model and a multi-objective optimization method established, the heat exchanger network and heat exchanger physical structure were designed and optimized. The results show that, pursuing a higher gross electrical efficiency leads to a decline in heat output. The electrical efficiency can be improved by increasing the external reforming ratio while ensuring self-sufficiency in heat. The heat integration is critical to enhance system performance, and optimizing heat exchanger network can make full use of the heat of stack exhaust and reduce the demand for external cold utility. The heat exchanger structural design has a trade-off between the total heat-transfer coefficient and the pressure drop. The net electrical efficiency of the three special solutions can reach 53.9 %, 65.7 %, and 65.8 %, respectively. The design of the maximum heat point (MHP) scheme can be considered when pursuing lower cost, and the design of the maximum power point (MPP) scheme can be employed for higher performance. [ABSTRACT FROM AUTHOR]

• A combined cycle system with intermediate recuperated gas turbine is proposed. • The load range of constant turbine inlet temperature operating mode is extended. • Gas turbine and combined cycle part-load efficiency is improved by 2.15% and 1.04%. • Effects of pressure drop and minimum recuperative flow on performance are analyzed. In order to improve the performance of the combined cycle gas turbine (CCGT) under off-design conditions, an intermediate recuperated combined cycle gas turbine (IRCCGT) system was proposed, which was designed to suppress turbine inlet temperature (TIT) from decreasing as the load drops. In this system, a heat exchanger is installed between the third and fourth turbine stages, wherein a portion of the exhaust from the third turbine stage was used to heat the compressed air. In addition, the system-based operation strategy (maximizing the load range that employs constant TIT operation mode) was also analyzed. The results indicate that the TIT can be maintained at the design value until the gas turbine power load is reduced to 49% of the design value. When the inlet guide vane (IGV) angle reached the minimum value, the IRCCGT system increased gas turbine efficiency and combined cycle electrical efficiency by 4.7 and 3.1 percentage points. At the same gas turbine (GT) load, the maximum gains of GT efficiency and combined cycle efficiency were 2.15 and 1.04 percentage points, respectively. The pressure drops in the recuperator had a great impact on system performance, while the minimum recuperative mass flow rate had little effect. Overall, the proposed IRCCGT system can reduce the slope of the efficiency and load curve and improve the operating performance of the system under off-design conditions. [ABSTRACT FROM AUTHOR]

A partially recuperative gas turbine combined cycle (GTCC pr ) is proposed in this paper to improve the off-design performance of power plants. The performance coupling with a new operation strategy is also analyzed. In the proposed GTCC pr , the gas flow at the outlet of the turbine is divided into two streams, and only a part of exhaust gas from the turbine is used to preheat the outlet air of the compressor. Exhaust gas streams from the recuperator are mixed with flue from the second reheater at the inlet of the first reheater to achieve similar temperature level. Specifically, the fraction of exhaust gas that preheats air can be changed to adjust the load of the combined cycle. The PG9351FA gas turbine unit is selected as the reference unit for comparison. Then, the design/off-design characteristics of the two cycles are compared and analyzed with the same turbine initial temperature. Results indicate that the partially recuperative GTCC pr running with the new operation has better off-design performances than the reference unit with approximately 1.7% maximum difference of efficiency. At the design point, the exhaust gas used for partial recuperation only accounts for 10% of the total mass, and the effect of recuperation is not evident. Therefore, the two cycles possess nearly similar output and efficiency. The efficiency of partially recuperative GTCC pr is nearly unchanged with the increasing recuperative mass fraction, which changes its specific power to adjust the load. At low loads, with decreasing turbine exhaust gas temperature, the efficiency improvement also decreases due to the partial recuperation. A comprehensive comparison with the reference unit revealed that GTCC pr with the proposed “recuperation adjustment” method can maintain a higher off-design efficiency and slightly lower design power output compared with the conventional cycle. Specific power adjustment of recuperation is one of the efficient methods for load adjustment, and GTCC pr is one of the best options. [ABSTRACT FROM AUTHOR]

A novel method for the combined cycle retrofitted with compressor inlet air heating (HEAT) process is proposed in this work for part load performance improvement. The performance of the new cycle is researched with two regulations with HEAT and compared with another two strategies with compressor inlet guide vane (IGV). For the novel method, the compressor inlet air is preheated by part of the exhaust flue gas from the heat recovery steam generator. Moreover, comparation result indicates that the novel strategy with HEAT to maintain design turbine inlet temperature (T3) and then to keep turbine exhaust temperature (T4) at its maximum value (HEAT-T3-T4) is suggested for load arrangement. If being compared with the cycle using IGV control to maintain design T3 then keep extreme T4 (IGV-T3-T4), a maximum combined cycle efficiency increment as 1.7% pt. could be obtained by the cycle with HEAT-T3-T4. Both energy analysis and exergy analysis are given in this paper. The simulation results indicate that higher compressor outlet temperature (T2) decreases the extra exergy destruction during combustion, so that the performance of the cycle with HEAT is improved. Meanwhile the specific work of each cycle has also been presented. Furthermore the pressure loss affection of the compressor inlet air heat exchanger on the combined cycle performance is investigated in range of 0%–5%. Each 1% pressure loss is calculated to decrease 1.4% on the design power output, and 0.25% pt. on the combined cycle efficiency, which will weaken the performance improvement. To summarize, this paper proposes a novel method for the combined cycle power output adjustment to obviously improve its part load efficiency. This innovative solution has never been suggested before and it could be combined with other methods for better result. • Compressor inlet air heating is purposed for cycle load regulation. • Waste energy can be recovered and exergy loss can be partly reduced by the method. • New method is compared with IGV control by two pairs of operation strategies. • 1.1% pt. - 1.7% pt. efficiency increment is achieved at cycle load 45%–100%. [ABSTRACT FROM AUTHOR]